Rain water treating device in combined sewage, backwashing method therefor

ABSTRACT

The present invention is aimed at treating rainwater in a combined sewer system, while enabling removal of a majority of pollution substances even if a large amount of entering rainwater. The invention relates to a rainwater-treating apparatus in a combined sewer system, said apparatus comprising a plurality of upward flow type high-speed filter vessels each having a layer of a floating filter medium, a common treated water vessel which is located at upper faces of said high-speed filter vessels and is adapted to collect treated water from the high-speed filter vessels, a used wash water vessel which collects used wash water from said high-speed filter vessels, a rainwater inflow channel for distributing the entering rainwater into upper portions of the high speed filter vessels, and rainwater inflow portions for flowing downwardly the rainwater distributed from the rainwater inflow channel under the respective floating filter media of the filter vessels.

TECHNICAL FIELD

[0001] The present invention relates to a rainwater-treating apparatusin a combined sewer system into which wastewater and storm water arecombined as a sewer in a confluent flow. The invention also relates to amethod for back washing said apparatus. The invention further relates toa sewer-treating system which uses the sewer-treating apparatus inraining (hereinafter referred to as “rainwater-treating apparatus). Inthe present application, the term “rainwater” is used to mean the sewerwhich is the combined flow of the storm water and the wastewater duringraining, therefore “rainwater” as a common meaning is discriminated from“storm water”.

BACKGROUND

[0002] In the combined sewer system for the wastewater and storm water,the flow amount largely varies between non-rainy weather and rainfallweather. In the combined flow type sewer-treating plant, the maximuminflow water amount per hour into the sewer-treating plant duringraining is controlled to three times 3Q as much as a design water amountQ that is the maximum inflow water amount per hour when there is nostorm water. An ordinary treatment can be effected in the same manner asin non-rainy weather if the water amount does not exceed Q. However, ifit is more than Q and not more than 3Q, this exceeds the ordinarytreating power of the reaction vessel in the treating plant, andtherefore a simple treatment is effected in which the rainwater issubjected to settlement treatment in the first sedimentation basin andthen discharged. Further, if the water amount increases and exceeds 3Q,the stormwater is actually discharged directly to a river, etc. withoutbeing treated at all.

[0003] Therefore, when the water amount increases over Q, almost allpollution substances are discharged to the river, etc. as they are. Thisresults in pollution of the environment. In particular, since thecombined sewer systems are employed particularly in many big cities inwhich the sewer systems have been propagated in early days, the aboveenvironmental problems have become manifesting with the development ofwaterfronts.

[0004] To cope with such problems, high-speed rainwater filterapparatuses having layers of floating filter media have been now beingpositively developed. However, since the thickness of the filter mediain the high-speed rainwater filter apparatuses now under investigationis not less than 2 m, and filter media outflow-preventing screens arenecessary at lower portions thereof. Alternatively, the apparatus isequipped with a flocculant-feeding mechanism to increase the treatingefficiency. In actual application, since a civil equipment, such as anexisting first sedimentation basin, having a water depth of 2.5 to 4 mcannot be used, the above filter apparatus is a technique that isrequired to be newly constructed from a civil structure, resulting in ahuge cost required.

[0005] The present invention solves the above problems of the prior art,and has been made to provide a rainwater-treating apparatus in thecombined sewer system which apparatus can remove a majority of thepollution substances even if rainwater exceeding Q enters or muchrainwater exceeding 3Q enter. Further, the present invention provides arainwater-treating apparatus which can be installed inexpensively byeasily modifying an existing first sedimentation basin as well as amethod for back washing the apparatus. Other object of the presentinvention is to provide the rainwater-treating apparatus in the combinedsewer system and the back washing method therefor, enabling theaccomplishment of the above object with almost no need of maintenance.

DISCLOSURE OF THE INVENTION

[0006] The present invention is made to solve the above problems, andits first aspect is to provide a rainwater-treating apparatus in acombined sewer system, said apparatus comprising a plurality of upwardflow type high-speed filter vessels each having a layer of a floatingfilter medium, a common treated water vessel which is located at upperfaces of said high-speed filter vessels and is adapted to collecttreated water from the high-speed filter vessels, a used wash watervessel which collects used wash water from said high-speed filtervessels, a rainwater inflow channel for distributing the enteringrainwater into upper portions of the high speed filter vessels, andrainwater inflow portions for flowing downwardly the rainwaterdistributed from the rainwater inflow channel under the respectivefloating filter media of the filter vessels.

[0007] The rainwater-treating apparatus according to the presentinvention can be constructed by partitioning a first sedimentation basinin the conventional combined flow type sewer-treating plant.

[0008] A second aspect of the present invention is to provide asewer-treating system in a combined flow type sewer-treating line, saidsystem comprising a first sewer-treating section and a secondsewer-treating section, said first sewer-treating section comprising asand-settling basin for receiving sewer, a first sedimentation basinprovided downstream of the sand-settling basin and a reacting vesselprovided downstream of the sedimentation basin, said secondsewer-treating section being provided downstream of the sand-settlingbasin and comprising a plurality of upward flow type high-speed filtervessels each having a layer of a floating filter medium, a commontreated water vessel which is located at upper faces of said high-speedfilter vessels and is adapted to collect treated water from thehigh-speed filter vessels, a used wash water vessel which collects usedwash water from said high-speed filter vessels, a rainwater inflowchannel for distributing the entering rainwater into upper portions ofthe high speed filter vessels, and rainwater inflow portions for flowingdownwardly the rainwater distributed from the rainwater inflow channelunder the respective floating filter media of the filter vessels,wherein when an amount of sewer to be treated is not more than a presetdesign water amount, the sewer is treated in the first sewer-treatingsection, whereas when the amount of the sewer to be treated is more thanthe preset design water amount, the sewer treatment is effected in thefirst sewer-treating section and in addition a portion of the sewerexceeding the preset design water amount is treated in the secondsewer-treating section.

[0009] The rainwater-treating apparatus can be installed by modifyingthe existing first sedimentation basin having a height of 2.5-4 m, forexample. The reason is as follows. That is, finer filter mediumparticles are used as compared with the conventional apparatus, thethickness of the floating filter medium layer can be made as thin asaround 0.5 to 1 m that is less than 2 m, no lower screen is required,and that an equipment for adding a flocculant is necessary.Consequently, the compact high-speed filter apparatus can beaccomplished, and a plurality of the high-speed filter vessels areprovided to reduce an amount of wash water to be used at one time,thereby the thickness of the common treated water vessel can be madethin. Further, the rainwater inflow channel preferably distributes therainwater as a spontaneous falling flow into the rainwater inflowportions of the respective high-speed filter vessels via inflow weirs ofthe channel so that variations in the water amount may be coped with.

[0010] According to a method for back washing the rainwater-treatingapparatus and the sewer system in the combined sewer system, backwashing is effected with respect to any high-speed filter vessel in therainwater-treating apparatus which filter vessel increased its presetpressure loss by flowing downwardly the treated water in the commontreated water vessel through the high-speed filtering vessel.

[0011] As mentioned above, according to the present invention, theupwardly flowing type high-speed filter vessels are provided throughpartitioning the first sedimentation basin in the combined flow typesewer-treating plant, and a large amount of the rainwater flowing induring raining is distributed into the vessels through the rainwaterinflow channel, so that the rainwater can be filtered at a high speedwith the charged floating filter medium. Therefore, even if therainwater enters in an amount of more than Q or if a large amount of therainwater enters in an amount exceeding 3Q, a majority of the pollutionsubstances can be removed. Furthermore, since the high-speed filtervessels and so forth are provided through partitioning a part of theexisting first sedimentation basins, a space for constructing andinstalling a new civil equipment is not required to be ensured. Asexplained below in more detail, the apparatus can be operated in thepresent invention with almost no maintenance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a plane view of an embodiment of the rainwater-treatingapparatus according to the present invention;

[0013]FIG. 2 is a vertically sectional view of FIG. 1;

[0014]FIG. 3 is a vertically sectional view of a rainwater inflowchannel;

[0015]FIG. 4 shows a plane view and sectional views showing the flow ofthe rainwater when raining starts;

[0016]FIG. 5 shows a plane view and sectional views showing the flow ofthe rainwater when raining continues;

[0017]FIG. 6 shows a plane view and sectional views showing the flow ofthe rainwater when raining continues and a vessel 1 is being backwashed;

[0018]FIG. 7 shows a filter medium piece having four plate-like arms tobe used in the present invention;

[0019]FIG. 8 shows a filter medium piece to be used in the presentinvention, in which wavy uneven portions are formed around an outerperipheral surface of a planar body having a rectangular sectionalshape;

[0020]FIG. 9 shows a filter medium piece having a Z-like sectional shapeto be used in the present invention;

[0021]FIG. 10 shows a tubular filter medium piece to be used in thepresent invention; and

[0022]FIG. 11 shows a wind wheel-type filter medium piece to be used inthe present invention, formed by modifying the blade portions of FIG. 7.

BEST MODE TO PRACTICE THE INVENTION

[0023] In the following, preferred embodiments of the present inventionwill be explained.

[0024]FIG. 1 is a plane view of the rainwater-treating apparatusaccording to the present invention, and FIG. 2 is a sectional view ofFIG. 1 cut along a line II-II. In this embodiment, a necessary portionof conventional first sedimentation basins 1 provided in the combinedflow type sewer-treating plant are left as they are (in the drawings,two rows are used as the first sedimentation basins), a plurality ofhigh-speed filter vessels 3 and used wash water vessels 4 are formed inthe remainder (in the drawings, two rows of the high-speed filtervessels and the used wash water vessels). As a result, the water area ofthe first sedimentation basins 1 decreases as compared with that in theconventional case. However, the smaller water area of the firstsedimentation basins 1 is recently sufficient with progress in thesewer-treatment technology as compared with the conventional case.Accordingly, in the combined flow type sewer-treating plants, thetreating powers of the first sedimentation basins 1 are often not fullyused. Thus, the invention arrangement makes no affect upon the ordinarysewer treatment. It may be said that since the first sedimentationbasins receive only up to the maximum sewer amount per hour duringnon-rainy weather, there is no influence upon the ordinary sewertreatment.

[0025] In a left side portion of FIG. 1 are provided a sand-settlingbasin 5 for receiving sewer and a rainwater vessel 6 and a wastewatervessel 7 into which sewer is distributed from the sand-settling basin,depending upon a design water amount and a rail falling amount. In somesewer-treating plants, the rainwater vessel 6 and the wastewater vessel7 are combined in the form of a common vessel. Conventionally, enteringsewer is entirely received in the sedimentation basin 5, and up to thedesign water amount 3Q is led to the conventional first sedimentationbasins 1 by wastewater pumps 8. Water from which suspended substances(SS) are separated in the first sedimentation basins 1 is led to adownstream reaction vessel where water is treated as conventionally.Since the entering amount of water is not more than Q, the above lineonly is operated in the same manner as in the conventional case. In thepresent invention, since the amount of the flowing-in water sometimesexceeds Q during raining, a portion of the water exceeding Q is entirelyled to of the high-speed filter vessels 3. Therefore, water feed pipesfrom the wastewater pumps 8 are modified to be led to the high-speedfilter vessels 3, if necessary.

[0026] The high-speed filter vessel 3 is a filter vessel in which ascreen 10 is stretched in a middle portion and a floating filter medium11 is charged under the screen 10. In this embodiment, totally eightfilter vessels are arranged in two rows, but the number of the vesselsis arbitrary, although plural is necessary. These high-speed filtervessels 3 are upwardly flowing type filter vessels. As shown in FIG. 3,a vertical rainwater inflow portion 12 is provided for each filtervessel. Rainwater is fed to a lower portion of the vessel through therainwater inflow portion 12, and inclusions and SS are captured and thetreated water discharged upwardly, while the sewer upwardly passes alayer the floating filter medium 11 charged. As shown, a common treatedwater vessel 13 is provided at upper faces of the high-speed filtervessels. The treated water flows in the treated rainwater channel 14from an end of the common treated water vessel 13 (from a right endportion in the drawings, and then discharged to a river, etc. In thisembodiment, each four filter vessels are connected to a single commontreated water vessel 13. Since a simple treated water bypass waterdischarge path is provided at an outflow portion of the usual firstsedimentation basins, the discharge path can be modified into thetreated rainwater water channels.

[0027] A rainwater inflow channel 15 is provided above the high-speedfilter vessels 3 to distribute rainwater into the above-mentionedrainwater inflow portions 12. The rainwater inflow channel 15 isarranged at such a high position to ensure a water level correspondingto a loss water head. For example, inflow weirs of the rainwater inflowchannel 15 are set higher than the water surface of the common treatedwater vessel 13 by around 0.2 to 1 mm. When a first flush treatment isto be effected during raining, the filter loss water head can be sethigher within this range. On the other hand, when treatment is effectedfor a long time period during no rainy weather after raining, it can beset lower in this range. Rainwater is raised into the rainwater inflowchannel 15 with the above rainwater pumps 8 and if necessary thewastewater pump 8, and is distributed and spontaneously flown down intothe rainwater inflow portions 12 of the high-speed filter vessels 3 viathe inflow weirs 16 provided in the rainwater inflow channel 15.

[0028] As mentioned above, a portion of the entering water exceeding Qduring raining is entirely raised into the rainwater inflow channel 15by the rainwater pumps 9 and if necessary the pumps 8. Therainwater-treating apparatus according to the present invention can copewith the amount of the entering water largely exceeding 3Q (for example,5Q to 7Q). However, abnormal huge rainfall may exceed the treating powerof the apparatus. In view of this, a rainwater bypass gate 17 ispreferably provided in a terminal end, for example of the rainwaterinflow channel 15 to overflow excess rainwater. Excess rainwater isflown down into the treated rainwater channel 14, and is dischargeddirectly to the river or the like. The rainwater bypass gate 17 may bepreliminarily set at an arbitrary height.

[0029] The floating filter medium 11 to be used in the present inventionis made preferably of a foamed polymer having an apparent density of 0.1to 0.4, a 50% compression hardness of not less than 0.1 MPa. As thefoamed having such physical properties, polypropylene, polystyrene,polyethylene, etc. may be recited. Among them, closed cell type foamedpolyethylene having the foamed degree controlled is preferred from thestandpoint of heat resistance, chemical resistance and weatherresistance.

[0030] If the apparent density of the floating filter medium 11 is lessthan 0.1, a desirable compression hardness cannot be obtained and thecharged layer of the floating filter medium is difficult to swell onback washing. On the other hand, if it is more than 0.4, it is fearedthat the filter medium may be downwardly flown away on back washing.Further, if the 50% compression hardness is less than 0.1 MPa, thefilter medium is compacted on filtering at a high speed, so that a largeamount of SS cannot be captured. The 50% compression hardness means apressure required to crush the filter medium to a half of its height.

[0031] The floating filter medium 11 to be used in the present inventionis preliminarily constituted by filter medium pieces having sizes of 4to 10 mm with uneven shapes or cylindrical shapes. The uneven shapemeans not a simple shape such as cubic or sphere but strange shapehaving some uneven portions at its outer surface. The floating mediumpieces 11 having such uneven shapes have the advantage that they formnon-linear large gaps among them, so that a large amount of SS can becaptured. Further, the floating filter medium pieces 11 havingcylindrical or columnar shapes also have the advantage that they cancapture a large amount of SS.

[0032] FIGS. 7 to 11 illustrate filter medium pieces to be used in thepresent invention by way of example. FIG. 7 shows a filter medium piecehaving four plate-like arms 9. FIG. 8 shows a filter medium piece inwhich wavy uneven portions are formed around an outer peripheral surfaceof a planar body having a rectangular sectional shape. FIG. 9 shows afilter medium piece having a Z-like sectional shape. FIG. 10 shows atubular filter medium piece. FIG. 11 shows a wind wheel-type filtermedium piece formed by modifying the blade portions of FIG. 7.

[0033] If the size of the floating filter medium piece 11 is smallerthan 4 mm, it is likely to cause clogging, and unsuitable for high-speedfiltering. If it is larger than 10 mm, the capturing efficiency of SSdecreases. The size in the case of strange-shape floating filter mediumpiece 11 means the maximum outer diametrical dimension. In addition tothe above mentioned floating filter medium pieces 11, spherical filtermedium pieces having a smaller apparent density can be charged.

[0034] The high-speed filter vessel 3 in which such floating filtermedium pieces 11 are charged can capture a large amount of SS, free fromcompacting of the filter medium, so that a large amount of the rainwatercan be treated at high speed. However, as the captured amount of SSincreases, the pressure loss increases to decrease the filtering power.This comes to require back washing. Therefore, a used wash waterdischarge valve 18 is provided in a bottom portion of each high-speedfilter vessel 3 so that water in a lower portion of the vessel may bedischarged into the used wash water vessel 4 via a used wash water pipe19. That is, if the used wash water valve 18 of any high-speed filtervessel 3 is opened, treated water inside the upper common treated watervessel 13 downwardly flows back into the high-speed filter vessel 3having the used wash water valve 18 opened, thereby back washing thecharged layer of the filter medium 11. A water discharge pump 20provided in the used wash water vessel 4 leads the used wash water to awastewater flow-in channel 22 or into the conventional firstsedimentation basins 1, as shown in FIG. 1, where the used wash water istreated. In this embodiment, the used wash water valve 18 is used, butthe used wash water may be discharged by a siphon type water dischargepath without using the used wash water valve 18.

[0035] The high-speed filter vessels 3 in the present apparatus can bewashed with a secondary treated water (secondary treated water:waterwhich has been treated in the reaction vessel) in the sewer-treatingplant so as to prevent generation of offensive odors on stoppage. Forthis purpose, a secondary treated water feed pipe 21 is provided to feedthe secondary treated water into the common treated water vessel.

[0036] In the following, the rainwater-treating method with therainwater-treating apparatus according to the present invention will beexplained together with the back washing method.

[0037] First, since the combined amount of the sewer flowing in thesand-settling vessel 5 is not more than Q at the time of non-rainyweather, the entire sewer is led to the conventional first sedimentationbasins 1 by the wastewater pumps 8, and it is treated there in the samemanner as in the conventional case.

[0038] If the combined sewer amount flowing in the sand-settling vessel5 exceeds the design water amount Q when it starts raining, an excessportion of the rainwater is entirely raised to the rainwater inflowchannel 15 by the rainwater pumps 9 and if necessary the wastewaterpumps 8. Then, the excess water spontaneously flows down and isdistributed into the rainwater inflow portions 12 of the respectivehigh-speed filter vessels 3 via the inflow weirs 16 as shown in FIG. 4.The distributed rainwater once flows down under the filter medium layer,and then upwardly flows and is filtered through the filter medium layerof the high-speed filter vessel 3, and the treated water is dischargedto the river, etc. via the common treated water vessel 13 and thetreated rainwater channel 14.

[0039] As mentioned above, the rainwater-treating apparatus according tothe present invention can filter a large amount of the rainwater at ahigh speed. Even if the amount of rainwater varies, a portion of thewater exceeding the design water amount Q can be entirely filtereddepending upon variations in the variations in rainwater, unless theamount of entering water abnormally increases. Since the SS removalpercentage of the high-speed filter vessel in the present invention isabout 70%, a majority of the pollution substances can be removeddifferent from the conventional case even if a large amount of rainwaterenters exceeding 3Q.

[0040] When rainfall continues, the pressure loss of each of thehigh-speed filter vessels 3 gradually increases. However, such increasesusually vary. The pressure loss of each of the high-speed filter vessel3 can be known from a difference in water level between the commontreated water vessel 13 and the rainwater inflow portion. However, sincethe water level of the common treated water vessel 13 is the same forthe filter vessels, increase in pressure loss of each filter vessel canbe grasped through increase in the water level of the rainwater inflowportion. FIG. 5 illustrates this state by way of example wherein thepressure loss of the ultra left side increases and the water level ofthe rainwater inflow portion 12 conspicuously increases as compared withthe other vessels. As a result, although the rainwater inflow waterlevel rises near the water level of the rainwater inflow channel 15. Ata point of time when the filter medium reaches near a preset pressureloss or the water level of the rainwater inflow portion reaches a presetwater level, washing is automatically started.

[0041] In this way, when it rains continuously like this, the pressureloss of all the high-speed filter vessels 3 gradually increases andcannot effect filtering sooner or later. The high-speed filter vessels 3are successively back washed when they reach the pressure lossrepresenting the above-mentioned automatically washing timing. Asmentioned above, back washing is effected by opening the used wash watervalve 18 in the bottom portion and downwardly flowing the treated waterin the common treated water vessel 13. FIG. 6 shows this state in whichthe ultra left vessel is under back washing. As mentioned above, whenthe floating filter medium 11 having the apparent density of 0.1 to 0.4is used for example, the filter medium can be effectively prevented frombeing discharged together with the back wash water. The back wash waterenters the used back wash water vessel 4, and the water discharge pump20 leads the used wash water to the conventional wastewater inflowchannel 2 or the first sedimentation basins 1 for treating it. In thisway, back washing is spontaneously effected only by opening the usedwash water valve 18 without operating any washing pump, etc. Even duringwashing, rainwater continuously flows in through the rainwater inflowportion 12, and high-speed filtering is continued in the high-speedfiler vessels other than that under washing, so that the treated wateris always fed into the common treated water vessel 13. On the otherhand, although the time required for back washing one vessel dependsupon the thickness of the filter medium, around 1 to 2 minutes arerequired for the thickness of the filter medium being 0.5 to 1 m.

[0042] As shown in FIG. 6, the second vessel from the ultra left vessel,which is under washing, reaches the back washing timing, althoughunusually. In this case, the second vessel from the left side is waitingfor washing until the ultra left vessel finishes washing and the waterlevel of the common treated water vessel 13 reaches a preset level. Insuch a case, when this vessel continues the treatment, the water levelof the rainwater inflow portion 12 may become the same as that of therainwater inflow channel 15 at the maximum due to further increase inpressure loss. In this case, since the water is treated in this vesselonly in an amount corresponding to the pressure loss of the filtermedium in this vessel, the moving amount of the water into the rainwaterinflow portion from the rainwater inflow channel 15 decreases ascompared with that in the other vessels. In this case, the decreasedamount of water enters the rainwater inflow portions 12 of the othervessels, and is treated there. Therefore, even if the back wash timinghappens to overlap like this, completely no maintenance managing controlis effected regarding the operation of introduction of the rainwater.Further, the washing time is around 2 minutes as mentioned above in thepresent invention, the washing-waiting time causes no actual problem.

[0043] As explained above, while the vessels which reach the presetpressure loss level are successively back washed, rainwater iscontinuously treated. Even if a special flow rate control is noteffected, the inflow amounts to the respective high-speed filter vessels3 are spontaneously adjusted.

[0044] Further, when the amount of entering water abnormally increases,excess rainwater is flown down into the rainwater-treating channel 14from the rainwater bypass gate 17 provided at the terminal end of therainwater inflow channel 15, and then directly discharged to the river,etc. Since the height of the rainwater bypass gate 17 is preliminarilyadjusted, no special operation is unnecessary on raining.

[0045] When rainfalling ends and the amount of the entering waterdecreases, the inflow amount of the rainwater into the high-speed filtervessels 3 spontaneously decreases. However, it is impossible topreliminarily anticipate the timing when the inflow water amount becomeszero, so that the filtration spontaneously ends in the state that thepollution substances stay in the filter media in the high-speed filtervessels 3, although the staying degree varies among the vessels. In thisway, completely no water enters the high-speed filter vessels 3 onnon-rainy weather. However, if this state is left as it is, offensiveodors may be generated from the pollution substances in the filtermedia. Under the circumstances, the secondary treated water in thesewer-treating plant is fed into the common treated water vessel 13 viathe secondary treated water feed pipe 21 so that the high speed filtervessels 3 are separately and successively back washed. When the commontreated water 13 reaches a preset water amount with the secondarytreated water, the used wash water valve 18 is opened to completely washan arbitrary one high-speed filter vessel 3. By repeating such steps,all the high-speed filter vessels 3 are completely washed. Since thiswashing completely washes the filter media with use of the secondarytreated water different from the above-mentioned filtration on rainyweather, the high-speed filter vessels wait for next inflow of rainwater

[0046] As explained above, in the rainwater-treating apparatus in thecombined sewer system and the sewer-treating system using thisrainwater-treating apparatus according to the present invention, almostall inflow rainwater exceeding Q which has formerly simply treated ornot treated can be filtered, which can contributes the environmentalclarification of the rivers, etc. Further, since the rainwater-treatingapparatus of the present invention can be provided by partitioning thefirst sedimentation basin in the combined flow type sewer-treatingplant, a space for constructing and installing a new civil equipment isadvantageously not required to be ensured. Further, therainwater-treating apparatus according to the present invention isalmost free from maintenance, and the flow rate can be spontaneouslyeffected without requiring operation which a worker must do particularlydepending upon changes in rain amount during storming. Therefore, sincemanagement is easy, and accordingly there is no increase in chemicalcosts, electric power costs, labor costs, etc. Furthermore, according tothe back washing method, each high-speed filter vessel can be backwashed by utilizing the treated water in the common treated water vesselwithout stopping the operation of the entire apparatus, while generationof offensive odors, etc. are completely prevented.

INDUSTRIAL APPLICABILITY

[0047] The present invention relates to the rainwater-treating apparatusto be used for treating sewer in the combined sewer system for sewer andstorm water and also to the sewer-treating system using thisrainwater-treating apparatus. The invention can ensure the treatment ofthe sewer in the combined sewer systems which have been recentlyincreasing. Thus, the invention has great industrial applicability incontributing the environmental clarification for rivers, etc.

What is claimed is:
 1. A rainwater-treating apparatus in a combinedsewer system, said apparatus comprising a plurality of upwardly flowing,high-speed filter vessels each having a layer of a floating filtermedium, a common treated water vessel which is located above saidhigh-speed filter vessels and is adapted to collect treated water fromthe high-speed filter vessels, a used wash water vessel which collectsused wash water from said high-speed filter vessels, a rainwater inflowchannel for distributing the rainwater into upper portions of the highspeed filter vessels, and rainwater inflow portions for flowingdownwardly the distributed rainwater from the distributed rainwaterinflow channel under the respective floating filter media of the filtervessels.
 2. The rainwater-treating apparatus claimed in claim 1, whichis constructed by partitioning a first sedimentation basin in thecombined sewage-treatment plant.
 3. The rainwater-treating apparatusclaimed in claim 1 or 2, wherein the rainwater inflow channelsdistribute the rainwater as a spontaneous falling flow into therainwater inflow portion of each of the high-speed filter vessels via aninflow weir.
 4. The rainwater-treating apparatus claimed in any one ofclaims 1 to 3, which further comprises a rainwater bypass gate providedin a rainwater inflow channels and adapted for overflowing excessrainwater into the rainwater inflow channels while bypassing thehigh-speed filter vessels.
 5. The rainwater-treating apparatus claimedin any one of claims 1 to 4, which further comprises a secondary treatedwater feed pipe for feeding a secondary treated water in thesewage-treatment plant into the common treated water vessel duringstoppage of the treatment of the rainwater.
 6. A sewer-treating systemin a combined sewer-system, said system comprising a firstsewer-treating section and a second sewer-treating section, said firstsewer-treating section comprising a sand-settling basin for receivingsewer, a first sedimentation basin provided downstream of thesand-settling basin and a reacting vessel provided downstream of thesedimentation basin, said second sewer-treating section being provideddownstream of the sand-settling basin and comprising a plurality ofupward flow type high-speed filter vessels each having a layer of afloating filter medium, a common treated water vessel which is locatedat upper faces of said high-speed filter vessels and is adapted tocollect treated water from the high-speed filter vessels, a used washwater vessel which collects used wash water from said high-speed filtervessels, a rainwater inflow channel for distributing the enteringrainwater into upper portions of the high speed filter vessels, andrainwater inflow portions for flowing downwardly the rainwaterdistributed from the rainwater inflow channel under the respectivefloating filter media of the filter vessels, wherein when an amount ofsewer to be treated is not more than a preset design water amount, thesewer is treated in the first sewer-treating section, whereas when theamount of the sewer to be treated is more than the preset design wateramount, the sewer treatment is effected in the first sewer-treatingsection and in addition a portion of the sewer exceeding the presetdesign water amount is treated in the second sewer-treating section. 7.The sewer-treating system claimed in claim 6, wherein said secondsewer-treating section is constructed by partitioning a firstsedimentation basin in the combined flow type sewage-treatment plant. 8.The rainwater-treating system claimed in claim 6 or 7, wherein therainwater inflow channels distribute the rainwater as a spontaneousfalling flow into the rainwater inflow portion of each of the high-speedfilter vessels via an inflow weir.
 9. The rainwater-treating systemclaimed in any one of claims 6 to 8, which further comprises a rainwaterbypass gate provided in a rainwater inflow channels and adapted foroverflowing excess rainwater into the rainwater inflow channels whilebypassing the high-speed filter vessels.
 10. The rainwater-treatingsystem claimed in any one of claims 6 to 9, which further comprises asecondary rainwater treated water feed pipe for feeding a secondarytreated water in the sewage-treatment plant into the high-speed filtervessels during stoppage of the treatment of the rainwater.
 11. Therainwater-treating system claimed in claims 6 to 10, wherein said firstsedimentation basin is provided downstream of the sand settling basinvia a first sewer vessel, and the second sewer-treating section isprovided downstream of the sand-settling basin via a second sewervessel.
 12. The rainwater-treating system claimed in claim 11, whereinthe first sewer vessel and the second sewer vessel are constituted by asingle common sewer vessel.
 13. A method for effecting back washing therainwater-treating apparatus in the combined sewer system claimed in anyone of claims 1 to 5 with respect to any high-speed filter vessel whichexceeds a preset pressure loss by flowing downwardly the treated waterin the common treated water vessel through the high-speed filteringvessel.
 14. The method for back washing the rainwater-treating apparatusclaimed in claim 13, which back washing said plurality of the high-speedfilter vessels by feeding a secondary treated water in thesewer-treating plant and flowing downwardly the secondary treated waterinto the common treating vessel during the stoppage of the treating therainwater.
 15. A method for effecting back washing therainwater-treating system in the combined sewer system claimed in anyone of claims 6 to 12 with respect to any high-speed filter vessel whichexceeds a preset pressure loss by flowing downwardly the treated waterin the common treated water vessel through the high-speed filteringvessel.
 16. The method for back washing the rainwater-treating systemclaimed in claim 15, which back washing said plurality of the high-speedfilter vessels by feeding a secondary treated water in thesewer-treating plant and flowing downwardly the secondary treated waterinto the common treating vessel during the stoppage of treating therainwater.